Goal-directed fluid therapy

ABSTRACT

A method includes setting a hydration goal and administering a diuretic to the patient to induce increased urine flow and collecting urine expelled by the patient. The amount of urine expelled by the patient is determined based on the collected urine. The patient is infused with fluid from a fluid source. The amount of fluid infused into the patient is determined. Diuresis is induced by automatically and continuously adjusting the amount of fluid infused into the patient from the fluid source to meet the hydration goal based on the set hydration goal, the determined amount of urine expelled by the patient and the fluid infused.

RELATED APPLICATIONS

This application is a divisional application of prior U.S. patent application Ser. No. 12/798,940 filed Apr. 13, 2010 and claims priority there to under 35 U.S.C. §§119, 120, 363, 365, and 37 C.F.R. §§1.55 and 1.78, which latter application is a divisional of prior U.S. patent application Ser. No. 10/936,945 filed Sep. 9, 2004, now U.S. Pat. No. 7,938,817, and both of these applications are incorporated herein by reference.

FIELD OF THE INVENTION

This invention relates to a patient hydration system and method wherein the rate of hydration fluid delivered to the patient is automatically adjusted based on the urine output of the patient to maintain, as necessary, a zero, positive, or negative net fluid balance in the patient.

BACKGROUND OF THE INVENTION

There are many medical procedures in which proper hydration of the patient is critical. For example, it has been observed that dehydration increases the risk of radiocontrast nephropathy (RCN) when radiocontrast agents are injected into a patient during coronary and peripheral vascular catheterization procedures. RCN is the third most common cause of hospital-acquired renal failure. It occurs in over 5% of patients with any baseline renal insufficiency and in 50% of patients with preexisting chronic renal insufficiency and diabetes. Radiocontrast media has a variety of physiologic effects believed to contribute to the development of RCN. One of the main contributors is renal medullary ischemia, which results from a severe, radiocontrast-induced reduction in renal/intrarenal blood flow and oxygen delivery. The medullary ischemia induces ischemia and/or death of the metabolically active areas of the medulla responsible for urine formation, called the renal tubules. Medullary ischemia is attributed to the increase of oxygen demand by the kidney struggling to remove the radiocontrast media from blood plasma and excrete it from the body at the same time as the normal process of controlling the concentration of urine. Oxygen consumption in the medulla of the kidney is directly related to the work of concentrating urine. Since the presence of radiocontrast media in the urine makes it much more difficult for the kidney to concentrate urine, the work of the medulla outstrips the available oxygen supply and leads to medullary ischemia.

Although the exact mechanisms of RCN remain unknown, it has been consistently observed that patients with high urine output are less vulnerable to contrast injury. It is also clear that dehydration increases the risk of RCN, likely because urine (and contrast media inside the kidney) is excessively concentrated. As a result, patients predisposed to RCN are hydrated via intravenous infusion of normal saline before, during and after the angiographic procedure. Hydration is commonly performed at a conservative rate, especially in patients with existing heart and kidney dysfunction, since over-hydration can result in pulmonary edema (fluid in the lungs), shortness of breath, the need for intubation, and even death. Thus, the patients at highest risk for RCN are those least likely to receive the only proven therapy for preventing RCN (I.V. hydration) due to the unpredictability of side effects from I.V. hydration.

A major limitation to the more widespread use of the already known therapeutic, or optimal, levels of I.V. hydration is the current inability to balance the amount of fluid going into the patient to the amount of fluid being removed or excreted from the patient. It is possible to have a nurse measure a patient's urine output frequently but this method is impractical as nurses are often responsible for the care of many patients. In addition, the only accurate method of measuring urine output is to place a catheter into the patient's urinary bladder. Without a catheter, the patient must excrete the urine that may have been stored in the bladder for several hours. During this time, the amount of I.V. hydration can be significantly less than the amount of urine produced by the kidneys and stored in the bladder, leading to dehydration. Since patients do not normally have such a catheter during procedures using radiocontrast media, a valid measurement of urine output is not possible.

There seems to be indisputable scientific evidence that RCN in patients with even mild baseline renal insufficiency can lead to long term complications and even increased risk of mortality. This scientific knowledge has not yet been extended to daily clinical practice as routine monitoring of renal function post-catheterization is not performed and limits the identification of the known short-term clinical complications.

At the same time, there is a great deal of awareness in clinical practice that patients with serious renal insufficiency (serum creatinine (Cr)≧2.0) often suffer serious and immediate damage from contrast. Many cardiologists go considerable length to protect these patients including slow, overnight hydration (an extra admission day), administration of marginally effective but expensive drugs, or even not performing procedures at all.

There are approximately 1 million inpatient and 2 million outpatient angiography and angioplasty procedures performed in the U.S. per year (based on 2001 data). Based on the largest and most representative published studies of RCN available to us (such as Mayo Clinic PCI registry of 7,586 patients) we believe that 4% of patients have serious renal insufficiency (Cr≧2.0). This results in the initial market potential of 40 to 120 thousand cases per year from interventional cardiology alone. There is also a significant potential contribution from peripheral vascular procedures, CT scans and biventricular pacemaker leads placement. As the awareness of the RCN increases, the market can be expected to increase to 10% or more of all cases involving contrast.

According to the prior art, hydration therapy is given intravenously (I.V.) when someone is losing necessary fluids at a rate faster than they are retaining fluids. By giving the hydration therapy with an I.V., the patient receives the necessary fluids much faster than by drinking them. Also, dehydration can be heightened by hyperemesis (vomiting), therefore the I.V. method eliminates the need to take fluids orally. An anesthetized or sedated patient may not be able to drink. Hydration is used in clinical environments such as surgery, ICU, cathlab, oncology center and many others. At this time, hydration therapy is performed using inflatable pressure bags and/or I.V. pumps. A number of I.V. pumps on the market are designed for rapid infusion of fluids (as opposed to slow I.V. drug delivery) for perioperative hydration during surgery, ICU use and even emergency use for fluid resuscitation.

An infusion pump is a device used in a health care facility to pump fluids into a patient in a controlled manner. The device may use a piston pump, a roller pump, or a peristaltic pump and may be powered electrically or mechanically. The device may also operate using a constant force to propel the fluid through a narrow tube, which determines the flow rate. The device may include means to detect a fault condition, such as air in, or blockage of, the infusion line and to activate an alarm.

An example of a device for rapid infusion of fluids is the Infusion Dynamics (Plymouth Meeting, Pa.) Power Infuser. The Power Infuser uses two alternating syringes as a pumping engine. Since it is only intended to deliver fluids (not medication), the Power Infuser has accuracy of 15%. It provides a convenient way to deliver colloid as well as crystalloid for hydration during the perioperative period among other possible clinical settings. The Power Infuser provides anesthesiologists with the ability to infuse at rates similar to that seen with pressure bags, but with more exact volume control. The maximum infusion rate is 6 L/hr. It has the flexibility of infusing fluid at 0.2, 1, 2, 4 and 6 L/hr. A bolus setting of 250 mL will deliver that volume in 2.5 min. In a large blood loss surgical case, the use of Power Infuser enables large volumes of colloid to be delivered to restore hemodynamics.

It is also known in the art that loop diuretics such as furosemide (frusemide) reduce sodium reabsorption and consequentially reduce oxygen consumption of the kidney. They also reduce concentration of contrast agents in the urine-collecting cavities of the kidney. They induce diuresis (e.g., patient produces large quantities of very dilute urine) and help remove contrast out of the kidney faster. Theoretically, they should be the first line of defense against RCN. In fact, they were used to prevent RCN based on this assumption until clinical evidence suggested that they were actually deleterious. More recently, doubts have been raised regarding the validity of those negative clinical studies.

In two clinical studies by Solomon R., Werner C, Mann D. et al. “Effects of saline, mannitol, and furosemide to prevent acute decreases in renal function induced by radiocontrast agents”, N Engl J Med, 1994; 331:1416-1420 and by Weinstein J. M., Heyman S., Brezis M. “Potential deleterious effect of furosemide in radiocontrast nephropathy”, Nephron 1992; 62:413-415, as compared with hydration protocol, hydration supplemented with furosemide adversely affected kidney function in high-risk patients given contrast. Weinstein et al. found that furosemide-treated subjects lost 0.7 kg on average, whereas a 1.3-kg weight gain was noted in patients randomized to hydration alone, suggesting that in furosemide-treated subjects the hydration protocol has been insufficient and patients were dehydrated by excessive diuresis.

The clinical problem is simple to understand: diuresis is widely variable and unpredictable but the fluid replacement (hydration) at a constant infusion rate is prescribed in advance. To avoid the risk of pulmonary edema, fluid is typically given conservatively at 1 ml/hr per kg of body weight. The actual effect of diuretic is typically not known for 4 hours (until the sufficient amount of urine is collected and measured) and it is too late and too difficult to correct any imbalance. Meanwhile, patients could be losing fluid at 500 ml/hour while receiving the replacement at only 70 ml/hour. The effects of forced diuresis without balancing are illustrated in the research paper by Wakelkamp et al. “The Influence of Drug input rate on the development of tolerance to furosemide” Br J Clin. Pharmacol. 1998; 46: 479-487. In that study, diuresis and natriuresis curves were generated by infusing 10 mg of I.V. furosemide over 10 min to human volunteers. From that paper it can be seen that a patient can lose 1,300 ml of urine within 8 hours following the administration of this potent diuretic. Standard unbalanced I.V. hydration at 75 ml/h will only replace 600 ml in 8 hours. As a result the patient can lose “net” 700 ml of body fluid and become dehydrated. If such patient is vulnerable to renal insult, they can suffer kidney damage.

To illustrate the concept further, the effects of diuretic therapy on RCN were recently again investigated in the PRINCE study by Stevens et al. in “A Prospective Randomized Trial of Prevention Measures in Patients at High Risk for Contrast Nephropathy, Results of the PRINCE. Study” JACC Vol. 33, No. 2, 1999 February 1999:403-11. This study demonstrated that the induction of a forced diuresis while attempting to hold the intravascular volume in a constant state with replacement of urinary losses provided a modest protective benefit against contrast-induced renal injury, and importantly, independent of baseline renal function. This is particularly true if mean urine flow rates were above 150 ml/h. Forced diuresis was induced with intravenous crystalloid, furosemide, and mannitol beginning at the start of angiography.

The PRINCE study showed that, in contrast to the Weinstein study, forced diuresis could be beneficial to RCN patients if the intravascular volume was held in a constant state (no dehydration). Unfortunately, there are currently no practical ways of achieving this in a clinical setting since in response to the diuretic infusion the patient's urine output changes rapidly and unpredictably. In the absence of special equipment, it requires a nurse to calculate urine output every 15-30 minutes and re-adjust the I.V. infusion rate accordingly. While this can be achieved in experimental setting, this method is not possible in current clinical practice where nursing time is very limited and one nurse is often responsible for monitoring the care of up to ten patients. In addition, frequent adjustments and measurements of this kind often result in a human error.

Forced hydration and forced diuresis are known art that has been practiced for a long time using a variety of drugs and equipment. There is a clear clinical need for new methods and devices that will make this therapy accurate, simple to use and safe.

SUMMARY OF THE INVENTION

It is therefore an object of this invention to provide a patient hydration system and method.

It is a further object of this invention to provide such a system and method which prevents kidney damage in a patient.

It is a further object of this invention to provide such a system and method which protects the patient undergoing a medical procedure involving a radiocontrast agent from kidney damage.

It is a further object of this invention to provide such a system and method which incorporates a balancing feature intended to prevent dehydration, overhydration, and to maintain a proper intravascular volume.

It is a further object of this invention to provide a balanced diuresis method which automatically balances fluid loss in the urine.

It is a further object of this invention to provide such a system and method which is accurate, easy to implement, and simple to operate.

It is a further object of this invention to provide such a system and method which is particularly useful in the clinical setting of forced diuresis with drugs known as I.V. loop diuretics.

The invention results from the realization that radiocontrast nephropathy in particular and patient dehydration in general can be prevented by automatically measuring the urine output of the patient and adjusting the rate of delivery of a hydration fluid to the patient to achieve, as necessary, a zero, positive, or negative net fluid balance in the patient.

This invention features, in one aspect, a fluid management system for a patient. The system typically includes a console for mounting on an IV pole. The console includes an input for setting a desired fluid balance for a set therapy duration. A first attachment mechanism extends from the console for hanging a urine collection chamber. A second attachment mechanism extends from the console for hanging a source of hydration fluid. A weighing subsystem in the console is responsive to the first attachment mechanism for weighing the patient's urine output collected in the urine collection chamber and is responsive to the second attachment mechanism for weighing the source of hydration fluid. An infusion pump is integrated with the console and configured to pump hydration fluid from the source of hydration fluid into the patient. A controller in the console is responsive to the set desired fluid balance, the set therapy duration, and the weighing subsystem. The controller is configured to determine the patient's urine output based on the weight of the urine collection chamber, determine the amount of fluid infused into the patient, and control the infusion pump to inject hydration fluid into the patient based on the set desired fluid balance, the weight of the urine collection chamber, and the weight of the source of hydration fluid to achieve the desired fluid balance during the set therapy duration.

In one embodiment, the console may include a display which displays the elapsed time of the therapy duration and the current fluid balance. The system may include means for indicating, on the console, when the urine collection is empty. The system may include means for indicating, on the console, when the source of hydration fluid is low on fluid. The controller may be configured to determine the patient's urine output based on the rate of change of the weight of the urine collection chamber, calculate a desired infusion rate based on the determined rate of change of the weight of the urine collection chamber and the set desired fluid balance, and control the infusion pump to hydrate the patient based at least on the calculated desired infusion rate.

This invention also features a fluid management system including a console which includes an input for setting a desired fluid balance, a urine collection chamber, a weighing device for weighing the patient's urine output collected in the urine collection chamber, a source of hydration fluid, a pump associated with the console and configured to pump hydration fluid form the source of hydration fluid into the patient, and a controller in the console configured to: determine the patient's urine output based on the weight of the urine collection chamber, operate the pump, monitor the amount of hydration fluid injected into the patient based, and control the pump based on the set desired fluid balance, the amount of hydration fluid injected into the patient, and the determined patient urine output.

This invention also features a fluid management system for a patient including a console for mounting on an IV pole. The console includes an input for setting a desired fluid balance, a first attachment mechanism extends from the console for handing a urine collection chamber. A weighing device in the console is responsive to the first attachment mechanism for weighing the patient's urine output collected in the urine collection chamber. A controllable infusion pump is integrated with the console and configured to pump hydration fluid from a source of hydration fluid into the patient at a variable rate. A controller in the console is responsive to the set desired fluid balance and the weighing device. The controller is configured to determine the patient's urine output based on the rate of change of the weight of the urine collection chamber, calculate a desired infusion rate based on the determined rate of change of the weight of the urine collection chamber and the set desired fluid balance, and control the infusion pump to hydrate the patient based at least on the calculated desired infusion rate.

This invention further features a method of addressing contrast induced nephropathy. One method includes injecting a contrast agent into a patient, imaging the patient, and including diuresis to drive any contrast agent through the patient's kidneys to reduce its toxic effects on the kidneys and prevent damage to the kidneys. A desired fluid balance is set. Urine expelled by the patient is collected in a urine collection bag. The method typically includes weighing the urine collection bag, employing a pump to infuse the patient with fluid from a fluid source, weighing the fluid source, and automatically adjusting the pump based on the weight of the urine collection bag and the weight of the fluid source and controlling the amount of fluid infused into the patient based on the amount of urine expelled by the patient and the set desired fluid balance.

In another embodiment, the method may include the step of administering a diuretic to the patient. Collecting urine expelled by the patient may include catheterizing the patient. Catheterizing the patient may include inserting a urinary catheter in the urinary tract of the patient. Weighing the urine collection bag may include providing an indication when a urine collection bag has reached its capacity. The method may further include providing an indication when the fluid source is low on fluid.

The subject invention, however, in other embodiments, need not achieve all these objectives and the claims hereof should not be limited to structures or methods capable of achieving these objectives.

This invention also features a method of addressing contrast induced nephropathy for a patient who has had a contrast agent injected into the patient. The method includes collecting urine expelled by the patient, determining the amount of urine expelled by the patient based on the collected urine, infusing the patient with fluid from a fluid source, determining the amount of fluid infused into the patient, and inducing diuresis to dilute the concentration of any contrast agent in the patient by automatically adjusting the amount of fluid infused into the patient from the fluid source based on the determined amount of urine expelled by the patient to balance the amount of urine expelled by the patient with the amount of fluid infused into the patient.

This invention also features a method of driving a toxin through a patient's kidneys, the method including collecting urine expelled by the patient. The method includes determining the amount of urine expelled by the patient based on the collected urine, infusing the patient with fluid from a fluid source, determining the amount of fluid infused into the patient, and inducing diuresis by automatically adjusting the amount of fluid infused into the patient from the fluid source on the determined amount of urine expelled by the patient to balance the amount of urine expelled by the patient with the amount of fluid infused into the patient.

This invention also features a method of preventing kidney damage due to dehydration, the method including collecting urine expelled by the patient. The method includes determining the amount of urine expelled by the patient based on the collected urine, infusing the patient with fluid from a fluid source, determining the amount of fluid infused into the patient, and maintaining the patient's hydration level by automatically adjusting the amount of fluid infused into the patient from the fluid source based on the determined amount of urine expelled by the patient to balance the amount of urine expelled by the patient with the amount of fluid infused into the patient, increasing the patient's level of hydration by infusing additional fluid based on user settings over and above fluid infused to match the patient's urine output.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects, features and advantages will occur to those skilled in the art from the following description of a preferred embodiment and the accompanying drawings, in which:

FIG. 1 is a schematic view of an example of a patient hydration system in accordance with the subject invention;

FIG. 2 is a schematic view of one embodiment of a patient hydration system in accordance with the subject invention wherein the weight of the urine output by a patient is measured and used as an input to control the infusion rate of an infusion pump;

FIG. 3 is a schematic view of another embodiment of a patient hydration system in accordance with the subject invention wherein the controller and weighing mechanism are integrated in a single control subsystem unit;

FIG. 4 is a flow chart depicting one example of the software associated with the controller of this invention and the method of adjusting the infusion rate based on the amount of urine output by the patient; and

FIG. 5 is a schematic view showing another embodiment of the subject invention wherein a flow meter is used to determine the amount of urine output by the patient.

DISCLOSURE OF THE PREFERRED EMBODIMENT

Aside from the preferred embodiment or embodiments disclosed below, this invention is capable of other embodiments and of being practiced or being carried out in various ways. Thus, it is to be understood that the invention is not limited in its application to the details of construction and the arrangements of components set forth in the following description or illustrated in the drawings. If only one embodiment is described herein, the claims hereof are not to be limited to that embodiment. Moreover, the claims hereof are not to be read restrictively unless there is clear and convincing evidence manifesting a certain exclusion, restriction, or disclaimer.

Patient hydration system 10, FIG. 1 according to this invention includes urine collection system 12 connected to patient P. Infusion system 20 typically includes an infusion device such as infusion pump 22 (e.g., a peristaltic pump) connected to source 24 of infusion fluid 26 (e.g., saline) by tubing 28. I.V. needle 30 is inserted in a vein of patient P and is connected to infusion pump 22 via tubing 32.

A control system or hydration balance means 34 detects the amount of urine output by the patient and automatically adjusts the infusion rate of infusion pump 22 to achieve, as necessary, a zero, positive, or negative net fluid balance in the patient. Typically, urine collection system 12 includes catheter 14 (e.g., a Foley catheter) placed in the bladder B of patient P. Tubing 16 connects catheter 14 to meter 36. Controller 38, typically programmable, is responsive to the output of meter 36 and is configured to adjust the infusion rate of infusion pump 22.

In one example, meter 36, FIG. 1 is a weight measurement device such as scale 50, FIG. 2. Here, urine collection chamber 52 on scale 50 is connected to catheter 14 via tubing 16. Scale 50 outputs a signal corresponding to the weight of urine or the combined weight of urine and hydration fluid (in this case to maintain net-zero hydration, the scale reading should be maintained constant) or the difference between the weight of urine and the weight of hydration fluid in collection chamber 52 to controller 38. The patient hydration system of this invention may further include diuretic administration system 60 including a source 62 of a diuretic such as furosemide administered via I.V. 64 inserted in patient P and connected to source 62 via tubing 66. In alternative embodiment, tubing 66 can be connected to the patient P via hydration I.V. 30 using standard clinical techniques. Also, if desired, a urine pump such as, for example, peristaltic pump 70 can be used to urge urine from bladder B to collection chamber 52 and to automatically flush catheter 14 if it is occluded. The advantage of urine collection pump 70 is that collection chamber or bag 52 can be at any height relative to the patient P. As shown, chamber 24 containing the hydration fluid 26 can also be placed on scale 50 in an embodiment where differential weighing is used. The controller (38) electronics and software are capable of integrating urine output (for example every 15 or 30 minutes) and changing the infusion rate setting of the infusion pump 22 following an algorithm executed by the controller.

Electronic controller 22 may also incorporate a more advanced feature allowing the physician to set a desired (for example positive) hydration net goal. For example, the physician may set the controller to achieve positive net gain of 400 ml in 4 hours. Controller 38 calculates the trajectory and adjusts the infusion pump flow rate setting to exceed the urine output accordingly. For example, to achieve a positive net gain of 400 ml over 4 hour, controller 38 may infuse additional 25 ml of hydration fluid every 15 minutes in addition to the volume of urine made by the patient in each 15 minute interval.

In the embodiment of FIG. 3, the programmable controller and the weighing mechanism are integrated in controller unit 34″. The patient (see FIG. 1) is placed on the hospital bed or operating table 80. The hydration I.V. 30 and the urinary collection (Foley) catheter 14 are inserted using standard methods. The controller electronics and the infusion pump 22′ are integrated in the single enclosure of the control subsystem 34″ console 82. Console 82 is mounted on I.V. pole 84.

Control subsystem 34″ may also include electronic air detector 86 that prevents infusion of air into the patient. The air detector 86 is of ultrasonic type and can detect air in amounts exceeding approximately 50 micro liters traveling inside the infusion tubing 32. In one example, air detector 86 employs technology based on the difference of the speed of sound in liquid and in gaseous media. If an air bubble is detected, the pump 22′ is stopped almost instantaneously.

Console 82 may include one or more weight scales such as an electronic strain gage and other means to periodically detect the weight of the collected urine in chamber 52 and, if desired, the weight of the remaining hydration fluid in chamber 26. In the proposed embodiment, bag 52 with collected urine and the bag 24 with hydration fluid 26 are hanging off the hooks 90 and 92 connected to the balance. The bags with fluids are suspended from the hooks and a system of levers translates force to a scale such as strain gage 22′. The strain gage converts force into an electronic signal that can be read controller 34″. Suitable electronic devices for accurately measuring weight of a suspended bag with urine are available from Strain Measurement Devices, 130 Research Parkway, Meriden, Conn., 06450. These devices include electronics and mechanical components necessary to accurately measure and monitor weight of containers with medical fluids such as one or two-liter plastic bags of collected urine. For example, the overload proof single point load cell model S300 and the model S215 load cell from Strain Measurement Devices are particularly suited for scales, weighing bottles or bags in medical instrumentation applications. Options and various specifications and mounting configurations of these devices are available. These low profile single point sensors are intended for limited space applications requiring accurate measurement of full-scale forces of 2, 4, and 12 pounds-force. They can be used with a rigidly mounted platform or to measure tensile or compressive forces. A 10,000 Ω wheatstone bridge offers low power consumption for extended battery life in portable products. Other examples of gravimetric scales used to balance medical fluids using a controller controlling the rates of fluid flow from the pumps in response to the weight information can be found in U.S. Pat. Nos. 5,910,252; 4,132,644; 4,204,957; 4,923,598; and 4,728,433 incorporated herein by this reference.

It is understood that there are many known ways in the art of engineering to measure weight and convert it into computer inputs. Regardless of the implementation, the purpose of the weight measurement is to detect the increasing weight of the collected urine in the bag 52 and to adjust the rate of infusion or hydration based on the rate of urine flow.

Console 82 is also typically equipped with the user interface. The interface allows the user to set (dial in) the two main parameters of therapy: the duration of hydration and the desired net fluid balance at the end. The net fluid balance can be zero if no fluid gain or loss is desired. Display indicators on the console show the current status of therapy: the elapsed time 100 and the net fluid gain or loss 102.

The user interface may also include alarms 104. The alarms notify the user of therapy events such as an empty fluid bag or a full collection bag as detected by the weight scale. In one proposed embodiment, the urine is collected by gravity. If urine collection unexpectedly stops for any reason, the system will reduce and, if necessary, stop the IV infusion of fluid and alarm the user. Alternatively, the console can include the second (urine) pump (see pump 70, FIG. 2) similar to infusion pump 22. This configuration has an advantage of not depending on the bag height for drainage and the capability to automatically flush the catheter 14, FIG. 3 if it is occluded by temporarily reversing the pump flow direction.

FIG. 4 illustrates an algorithm that can be used by the controller software of controller 34″ to execute the desired therapy. The algorithm is executed periodically based on a controller internal timer clock. It is appreciated that the algorithm can be made more complex to improve the performance and safety of the device. Controller 34″, FIG. 3 is programmed to determine the rate of change of the urine weight, steps 110 and 112, FIG. 4 to calculate a desired infusion rate based on the rate of change of the urine weight, step 114, and to adjust the infusion rate of the infusion pump 22, FIG. 3 based on the calculated desired infusion rate, step 116, FIG. 4.

So far, the subject invention has been described in connection with the best mode now known to the applicant. The subject invention, however, is not to be limited to these disclosed embodiments. Rather, the invention covers all of various modifications and equivalent arrangements included within the spirit and scope of the appended claims. Particularly, the embodiments used to illustrate the invention use the weight of the collected urine for balancing. It is understood that it is the volume of the urine that is clinically important but the weight of the urine is equivalent for any practical purpose. For the purpose of this application, 100 grams of urine are the same as 100 ml of urine. It is believed at the time of the subject invention that measuring weight is more practical than measuring volume and that the weight is often used as a clinically acceptable substitute of volume of liquids that consist mostly of water. For practical purposes, the specific gravity (specific gravity of a substance is a comparison of its density to that of water) of urine and hydration fluids is the same as water. Those skilled in the art will realize that it is possible to measure volume directly using a meter which monitors the height of the column of the liquid in a vessel or by integrating the known volume of strokes of the pump over time. The exact meter used does not change the subject invention in regard to the balancing of urine output with hydration. Also, flow meter 36′, FIG. 5 could be used to measure the urine output of patient P and a signal corresponding to the flow rate provided to controller 38. Urine flow meter 36′, FIG. 5 can be one of the devices disclosed in U.S. Pat. Nos. 5,891,051; 5,176,148; 4,504,263; and 4,343,316 hereby incorporated herein by this reference.

Also a medical device manufacturer, SFM Ltd., 14 Oholiav Street, Jerusalem, 94467, Israel manufactures and markets an electronic flow meter suitable for use with this invention. According to the manufacturer SFM Ltd. the UREXACT 2000 System is an accurate electronic urine-measuring device that combines an innovative disposable collection unit with a re-usable automatic electronic meter to provide precise urine monitoring. The UREXACT 2000 is based on the ultrasonic method of measuring fluid flow.

Thus, although specific features of the invention are shown in some drawings and not in others, this is for convenience only as each feature may be combined with any or all of the other features in accordance with the invention. The words “including”, “comprising”, “having”, and “with” as used herein are to be interpreted broadly and comprehensively and are not limited to any physical interconnection. Moreover, any embodiments disclosed in the subject application are not to be taken as the only possible embodiments. Other embodiments will occur to those skilled in the art and are within the following claims.

In addition, any amendment presented during the prosecution of the patent application for this patent is not a disclaimer of any claim element presented in the application as filed: those skilled in the art cannot reasonably be expected to draft a claim that would literally encompass all possible equivalents, many equivalents will be unforeseeable at the time of the amendment and are beyond a fair interpretation of what is to be surrendered (if anything), the rationale underlying the amendment may bear no more than a tangential relation to many equivalents, and/or there are many other reasons the applicant can not be expected to describe certain insubstantial substitutes for any claim element amended. 

1. A method comprising: setting a hydration goal; administering a diuretic to the patient to induce increased urine flow; collecting urine expelled by the patient; determining the amount of urine expelled by the patient based on the collected urine; infusing the patient with fluid from a fluid source; determining the amount of fluid infused into the patient; inducing diuresis by automatically and continuously adjusting the amount of fluid infused into the patient from the fluid source to meet the hydration goal based on the set hydration goal, the determined amount of urine expelled by the patient, and the determined amount of fluid infused into the patient.
 2. The method claim 1 in which collecting urine expelled by the patient includes collecting urine expelled by the patient in a urine collection bag and determining the amount of urine expelled by the patient based on the collected urine includes weighing the urine collection bag.
 3. The method of claim 1 in which infusing the patient with fluid from a source includes employing a pump to infuse the patient with fluid from a fluid source.
 4. The method of claim 3 in which determining the amount of fluid infused into the patient includes weighing the fluid source.
 5. The method of claim 4 further including providing an indication when the fluid source is low on fluid based on the weight of the fluid source.
 6. The method of 1 in which adjusting occurs every 15 minutes or less for a therapy duration. 